Running an electric arc furnace for stainless means sizing the supply to the batch: melting 100 kg of steel to about 1,600 °C needs at least 36 kWh, so a 15 kW source takes several hours once losses are counted. Charge dry low-carbon scrap, strike the arc, hold the melt, decarburize before adding ferrochrome, and keep an emergency disconnect within reach of a second person at all times.
Part of Stainless Steel Production
Operating a small electric arc furnace for 50-200 kg heats of alloy steel: power, charging, melting, refining, tapping and the stops.
The Power Supply Sets The Batch Size
The corpus has no article on building an arc furnace; the carrier simply names it as the standard tool for 50-200 kg batches at about 1,600 °C. Two things limit what a village can run: the electrical supply, and the electrodes. For supply see Hydro Generator, which gives output as watts = head × flow × 9.81 × efficiency, with head in metres and flow in litres per second. For electrodes, baked carbon is made as in Carbon Electrode Production.
What You Need
- A furnace shell and refractory lining (Refractory Materials), with a taphole.
- Carbon electrodes and a mechanism to raise and lower them.
- A supply delivering the current in the worked example, with a disconnect and fuses sized for it.
- An oxygen or air lance (iron pipe) for decarburizing, per the carrier.
- Dry charge, dry tools, preheated ladle and moulds.
Method: One Heat
Step 1: Dry and charge. Load low-carbon scrap. Preheat if the furnace allows, so no moisture rides in.
Step 2: Strike the arc. Lower the electrode until the arc strikes; keep it stable as the charge slumps.
Step 3: Melt to about 1,600 °C (the carrier’s figure). A flat bath of liquid, not sparking piles of solid scrap, is the sign you are ready for the next step.
Step 4: Decarburize. Blow air or oxygen through the melt to bring carbon below 0.08%, as the carrier directs. See Carbon Control.
Step 5: Add alloys and adjust per Alloy Addition Sequence, then skim slag.
Step 6: Tap into a dry, preheated ladle and cast.
Worked Example
Energy to melt. I recall about 1.3 MJ is needed to heat and melt 1 kg of steel to roughly 1,600 °C (recalled handbook figure, not in the corpus). 1.3 MJ ÷ 3.6 MJ/kWh = 0.36 kWh/kg. For 100 kg that is 36 kWh, the floor with no losses.
With losses. Assume 50% of electrical input ends up in the steel (an assumption, not a measured figure for any furnace in this wiki): 36 / 0.5 = 72 kWh. At a constant 15 kW the heat takes 72 / 15 = 4.8 hours. A smaller supply stretches this; a supply that cannot overcome the furnace’s heat loss may never reach melt.
Current. Power = voltage × current. If the arc and circuit run at about 100 V (an assumed example, not a design), a 15 kW draw means 15,000 / 100 = 150 A. Conductors and joints for that current are sized on the Bus Bars rule of thumb of 1.5-2 A per mm² of copper: 150 / 2 = 75 mm² to 150 / 1.5 = 100 mm².
A hydro source for 15 kW. With 10 m head and 50% efficiency (examples), flow = 15,000 / (10 × 9.81 × 0.5) = 306 L/s. That is a real stream, not a trickle.
Common Mistakes
- Treating stainless as a quick melt. A 4.8-hour heat on a hydro supply ties up the stream and the crew.
- Leaving a wet tool in the bath. A single damp rod can eject metal.
- Lining with acidic refractory and loading chromium-rich slag. I recall chromium-rich slags attacking silica-based linings and that basic or chrome-based refractories are preferred; I cannot source this, so test the lining on a small heat.
Safety
Three stops, named
Electrical: a lockable disconnect on the supply side, outside the splash zone, with a second person stationed at it whenever the arc is struck. Molten metal: water or damp scrap in the melt, or a cold mould, flashes to steam and throws metal; all charge and tooling must be dry and preheated. Gas and light: decarburizing releases carbon monoxide (CO Risk); the arc emits ultraviolet and infrared that burn eyes, so shield with dark filter glass. The furnace has no safe coast-down: killing the supply stops the arc, but the bath stays at 1,600 °C for hours.
What’s Next
- Learn next: Carbon Control - the step that decides the grade
- Combine with: Alloy Addition Sequence - what goes in after refining